This invention relates to novel cured phenolic resins to be used as a friction particle material. It is especially useful where cashew nut shell oil friction particles, called "Cardolite" have been used in the past.
Novolac phenol aldehyde resins are phenol-ended chain polymers. They are formed by the reaction of an aldehyde with an excess of phenol in the presence of an acid catalyst and/or heat. They are thermoplastic, permanently soluble and fusible. However, upon the addition of a curing agent, they can be cured into an insoluble, infusible resin. Thus, novolac resins are known as "two-stage" resins.
Phenol aldehyde condensation products have been used as binders for abrasive materials. However, to our knowledge, the novel cured phenol aldehyde products of this invention have not been used as a friction particle per se.
As used herein "friction particle" is intended to mean having the properties of substantially no softening at elevated temperatures and will not flow together or cohere with other particles, as a "friction binder" would, or fuse with like friction particles. It is insoluble, having an acetone extraction of less than 10% and often less than 5%; it is infusible, i.e., has gone beyond the B stage, to the C stage. It will not melt at 700.degree. F. A friction particle is held in place with a friction binder.
As used herein, a "friction binder" has the properties of flowability, and has adhesive and cohesive bonding action and thereby binds together the asbestos and other additives (including a friction particle) necessary for building a brake lining or other similar article of manufacture. The binder, as supplied to the industry, will melt as a dry powder or is a liquid resin, and can be either an A stage or B stage resin. The binder becomes a C stage resin after it is combined with the other ingredients and cured.
This composition of the binder, friction particle and other additives, is heated to about 300.degree.-400.degree. Fahrenheit and pressed at about 500-2000 pounds per square inch in order to form a brake lining composition, or clutch facing or other braking device. Thus, the friction particle is substantially insoluble and infusible, softening only at elevated temperatures (i.e., above about 400.degree.-500.degree. Fahrenheit). Conventional "two stage" phenolic novolac resin can be used as a binder in the composition of the present invention.
It has now been found that a composition of matter, useful as a friction particle, can be prepared as a reaction product of an aromatic amine modified novolac resin cured in combination with a particular aromatic polycarboxylic compound. The friction particles have superior high temperature properties in brake lining compositions. Friction particles prepared from polymerized cashew nut shell liquids, known as Cardolites, are commonly used as friction particles but fade (loss of coefficient of friction) at temperatures as low as 700.degree.-800.degree. F. Substitution of the friction particles of the present invention extend the onset of fade from about 750.degree. F. to about 1000.degree. F. giving high utility in brake lining compositions and providing a recognized technical advance in the art in compositions having, e.g., about 15 to 30% by weight of phenolic novolac resin binder, about 30 to 60% by weight of asbestos, up to about 40% by weight of fillers and about 5 to 15% by weight of friction particles.